Refrigerant vapor compression systems are well known in the art and commonly used for conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems are also commonly used in transport refrigeration systems for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable items. Conventional refrigerant vapor compression systems include four basic components: a compressor, a refrigerant heat rejection heat exchanger, an expansion device and a refrigerant heat absorption heat exchanger that functions as a refrigerant evaporator. Depending upon whether the refrigerant vapor compression system is operating in a subcritical cycle or a transcritical cycle, the refrigerant heat rejection heat exchanger functions, respectively, as a refrigerant condenser or a refrigerant gas cooler. These basic refrigerant system components are interconnected by refrigerant lines in a closed refrigerant circuit, arranged in accord with known refrigerant vapor compression cycles, and operated in the subcritical pressure range for the particular refrigerant in use.
The compressor functions to compress low pressure, low temperature refrigerant vapor to a high pressure and high temperature refrigerant vapor. Whether the compressor is a reciprocating compressor, a scroll compressor, a rotary compressor or screw compressor, it includes a compression mechanism driven by a motor and having rotating or orbiting elements that interact to compress the refrigerant vapor passing through the compressor. It is common practice to include a lubricant in the compressor to reduce wear of the compression mechanism and its parts, as well as to seal gaps between the interacting elements to reduce refrigerant vapor leakage during the compression process. As the lubricant becomes heated due to exposure to the high temperatures generated in the compression process, its viscosity is reduced which impairs its friction reducing ability and its sealing effectiveness. Therefore, it is customary to provide for cooling of the lubricant.
For example, U.S. Pat. No. 5,899,091 discloses a refrigeration system wherein compressor lubricating oil is cooled by passing the lubricating oil in heat exchange relationship with the post-expansion economizer refrigerant flow. U.S. Pat. No. 6,058,727 discloses a refrigeration system wherein the compressor lubricating oil is passed through a heat exchange coil disposed in heat exchange relationship with refrigerant vapor leaving the evaporator to cool the lubricating oil.